Process for the preparation of a copolymer of maleic anhydride and an alkyl vinyl ether, copolymers of maleic anhydride and an alkyl vinyl ether and an apparatus

ABSTRACT

Process for the preparation of a copolymer of maleic anhydride and an alkyl vinyl ether, comprising the steps of supplying maleic anhydride and the alkyl vinyl ether and an initiator, together forming a feed flow, through an inlet to a reactor wherein maleic anhydride and the alkyl vinyl ether react to a copolymer of maleic anhydride an alkyl vinyl ether thereby forming a reaction mixture with the maleic anhydride, the alkyl vinyl ether and the initiator characterized in that the process is a continuous process and the reactor is a loop reactor wherein the reaction mixture is internally circulated, whereby this reaction mixture arrives at the inlet before the maleic anhydride and alkyl vinyl ether have completely reacted while a remainder of initiator is still present. The invention further relates to copolymer of maleic anhydride and alkyl vinyl ether, including hydrolyzed or alcoholized copolymers, characterized in that a molecular weight distribution, expressed as Mw/Mn, is less than 2. The invention also relates to an apparatus for conducting the process of the invention.

The present invention relates to a process for the preparation of acopolymer of maleic anhydride and an alkyl vinyl ether, comprising thesteps of supplying maleic anhydride and the alkyl vinyl ether and aninitiator, together forming a feed flow, through an inlet to a reactorwherein maleic anhydride and the alkyl vinyl ether react to a copolymerof maleic anhydride and an alkyl vinyl ether which forms a reactionmixture with the maleic anhydride, the alkyl vinyl ether and theinitiator.

The invention also relates to copolymers of maleic anhydride and analkyl vinylether and to an apparatus for conducting the process of theinvention.

A process for the preparation of a copolymer of maleic anhydride and analkyl vinyl ether is known from EP-A-0919577. In this publication, asemi-batch process is described in which three feeds, being maleicanhydride in a solvent, an alkyl vinyl ether, and a radical initiator ina solvent, are dosed gradually to a pre-charged reactor containing apre-polymerized copolymer consisting of the same monomers in a solvent.The example reads to a process where a reactor is pre-fed with anacetonic solution of a maleic anhydride/methyl vinyl ether copolymer,maleic anhydride and methyl vinyl ether to which, upon heating, is fedan acetonic solution of maleic anhydride, methyl vinyl ether and anacetonic solution of tert.-butylperneodecanoate. A copolymer with amolecular weight of 2,000,000 g/mol is obtained.

A disadvantage of the process as described in EP-A-0919577 is the factthat the reactor has to be precharged with a prepolymerised copolymer inorder to prevent a run-away of the reaction.

The object of the invention therefore is to provide a process thatexhibits a lower risk of a run away reaction, without the need ofprecharging the reactor with prepolymerised copolymer.

This object is achieved by the process of the invention, in that theprocess is a continuous process and the reactor is a loop reactorwherein the reaction mixture is internally circulated, whereby thisreaction mixture arrives again at the inlet before the maleic anhydrideand alkyl vinyl ether have completely reacted and while a remainder ofinitiator is still present.

With the process according to the invention there is a lower risk of arun away reaction, without the need of precharging the reactor withprepolymerised copolymer.

A further advantage of this process is that the temperature in theprocess can be better controlled and also that the process can beoperated at higher temperatures than in the known batch proces in orderto further reduce the production time. Another advantage of using a loopreactor is that the continuous production of the desired copolymers isless time consuming, especially when compared to the same reactor volumein a batch process, and can be operated more efficiently in anindustrial environment. This makes the process of the invention morecost effective.

The preparation of a copolymer of maleic anhydride, MA and alkyl vinylether, AVE, hereinafter referred to as a copolymerization, is generallyperformed with radicals through a radical reaction. The radicals areformed by an initiator.

In the process of the invention MA, and AVE, which are both referred toas monomers, an initiator, I, and an optional diluent, solvent orsolvent mixture are supplied through an inlet to a reactor whereby MAand AVE react to a copolymer of MA and AVE. The copolymer and MA, AVE, Iand optional additives form a reaction mixture.

The process of the invention is a continuous process whereby the feedflow of MA, AVE and I, including other optional additives as e.g. asolvent, is continuously added through an inlet to the reactor andwhereby continuously a part of the reaction mixture leaves the reactor.When the process is run under stationary conditions the flow of the partof the reaction mixture which is leaving the reactor equals the feedflow.

In the known processes for the copolymerization of MA and AVE, which arecarried out in a batch process, use is nowadays mainly made of asuspension process or a solution process. The continuous process of theinvention can be carried out in solution, in which case also a solventor a solvent mixture is present in the reaction mixture, or insuspension, in which case at least one diluent is present in thereaction mixture. A suspension process generally yields copolymer powderor pellets while a solution process yields a copolymer solution.

The reactor is a loop reactor in which the reaction mixture isinternally circulated in such a way that at the time the reactionmixture arrives at the inlet, where it is contacted with fresh suppliedMA, AVE and I, it is not yet completely converted. This means that theMA and AVE have not yet completely reacted and that a remainder ofinitiator is still present.

In the process of the invention a loop reactor of the commonly knownreactor types with an inlet and an exit and with some kind of internalcirculation in a loop can be applied. Normally this type of reactor iscompletely filled with liquid. Preferably a loop reactor with twoseparate, interconnected, jacketed reactors is used, whereby the loop isformed by connecting the exit of a first reactor with a tube to an inletof a second reactor from which a tube connects the exit of the secondreactor with the inlet of the first reactor. The separate jacketedreactors comprise mono or multi parallel tubes, whereby a circulationpump is fitted in the loop. Another preferred loop reactor is a stirredtank reactor with an internal draft tube. The internal draft tubecreates an annular part in the reactor and in the annular part a helixtype mixer, hereinafter referred to as helicon mixer, is placed.

In particular for a suspension process a loop reactor with two separatejacketed reactors and a circulation pump is preferred. For a solutionprocess this loop reactor concept can also be applied but a stirred tankreactor with external cooling of the feed flows is preferred since thisreactor is less sensitive to deposition of copolymer from the solution.

In the process of the invention the monomers MA and AVE are used. The MAis solid at room temperature and melts at 54° C. The MA can be fed tothe reactor as a melt or in a solutionin e.g. the AVE. Suitable alkylvinyl ethers for the process of the invention include methyl vinylether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether,butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, pentylvinyl ether, amyl vinyl ether, isoamyl vinyl ether, hexyl vinyl ether,n-octyl vinyl ether, 2-ethyl-hexyl vinyl ether, decyl vinyl ether,dodecyl vinyl ether, 2,3-dihydrofuran. Preferably the AVE is a C1-C4alkyl vinyl ether. Copolymers based on C1-C4 alkyl vinyl ethers arecommercially the most interesting because of their good solubility inwater. Most preferred is methyl vinyl ether, because it renders acopolymer with MA with the best solubility in water.

As initiator in the process of the invention, the usual radicalinitiators known in the art for copolymerization of MA and AVE areapplicable e.g. azo compounds, peroxy-ester, acyl peroxide and alkylperoxide compounds. Suitable initiators include for example2,2′-azobis(isobutyronitril), 2,2′-azobis(2,4-dimethylvaleronitril),2,2′-azobis(4-methoxy-2,4-dimethylvaleronitril), cumylperoxyneodecanoate (Trigonox® 99, AKZO-Nobel), tert-butylperoxyneodecanoate, tert-amyl peroxyneodecanoate, tert-butylperoxyneodecanoate (Trigonox® 23, AKZO-Nobel), tert-butylperoxyisononaoate, tert-butyl peroxy-3,5,5-trimethylhexanoate,2,4,4-trimetylpentyl peroxy-2-neodecanoate (Trigonox® 151, AKZO-Nobel),dilauryl peroxide, dioctanoyl peroxide, bis(4-tert-butyl-cyclohexyl)peroxydicarbonate (Perkadox® 16, AKZO-Nobel).

The process of the present invention can also be conducted attemperatures above 105° C., which is seen as an upper temperature forthe known batch wise processes. In the process of the invention ittherefore now is also possible to use azo compounds, peroxy-ester, acylperoxide and alkyl peroxide compounds with higher decompositiontemperatures. The one skilled in the art will be able to select suitableinitiators from these classes with the desired half life time at thereaction temperature. Examples include dibenzoyl peroxide (Lucidol®,AKZO-Nobel), tert-butyl peroxy-2-ethylhexanoate (Trigonox® 21,AKZO-Nobel), dicumyl peroxide (Perkadox® BC, AKZO-Nobel), di-tert-amylperoxide (Trigonox® 201, AKZO-Nobel), tert-butyl peroxybenzoate(Trigonox® C, AKZO-Nobel), tert-butyl peroxy-2-ethyl-hexylcarbonate(Trigonox® 117, AKZO-Nobel).

It is also possible to use a mixture of two initiators, one with a highdecomposition temperature under the given reaction conditions, e.g.higher than 105° C. and one with a lower decomposition temperature. Theadvantage of such a mixture of two initiators is that it is universallyapplicable at several reaction temperatures. Generally the molar ratioof MA/initiator is between 100 and 10.000, preferably between 500 and5000 and more preferably between 750 and 1250. Advantages thereof are agood balance between molecular weight and conversion.

Generally the feed flow comprises a molar ratio of AVE to MA of between1.05 and 5. The ratio is higher than 1.05 and preferably higher than 1.1in order to obtain a copolymer product with a low concentration ofunreacted MA. In a suspension process the AVE can also serve as adiluent in which case a molar ratio higher than 2 may be chosen.Preferably the molar ratio of alkyl vinyl ether to MA is less than 5.Higher ratios make the process of the invention less cost-effectivebecause a large amount of AVE has to be removed from the copolymerobtained.

The process according to the invention is generally carried out at atemperature between 50° C. and 180° C. At temperatures below 50° C., thecopolymerization becomes too slow. Above 180° C. degradation reactionsoccur more frequently. For a better balance between copolymerization anddegradation reactions the reactor temperature is preferably chosenbetween 70 and 150° C., and more preferably between 90 and 130° C.

In the process of the invention the temperature of the reactor increasesdue to the exothermic nature of the copolymerisation reaction. Coolingtherefore is preferred and the amount of cooling is chosen such that thecooling compensates for the released heat of reaction. Cooling can beperformed directly by cooling the reactor content, through e.g. a jacketor a coil, or indirectly by cooling of the feed flow to the reactor.Preferably the feed flow is cooled to below ambient temperature beforebeing introduced into the reactor because this gives a more efficientway of cooling the reactor than through a jacket or a coil. The processcan be carried out at atmospheric pressure. However if the process iscarried out at a temperature higher than the boiling point of one of thecomponents in the reaction mixture, the process is preferably carriedout under pressure. Absolute pressures of 1 to 20 bar can be used in theprocess. An inert gas can be used for obtaining the desired pressurelevel.

In the process of the invention a remainder of initiator is present atthe time that the internally circulated reaction mixture arrives at theinlet. This means that the fraction of initiator which has decomposedinto radicals after completing one circulation through the loop reactor,starting from the inlet, is less than 100%. The. fraction of decomposedinitiator is determined by the half-life time of the initiator at thetemperature in the loop reactor and the time required for the reactionmixture to complete one circulation through the loop reactor,hereinafter referred to as circulation time. The fraction of decomposedinitiator can be defined through the ratio of the circulation time inthe loop reactor to the half-life time of the initiator. When the ratioof the circulation time in the loop reactor to the half-life time of theinitiator is 1, the fraction of initiator, which has decomposed uponcompletion of one circulation in the loop reactor is 50%. When the ratioof the circulation time in the loop reactor to the half-life time of theinitiator is 3, the fraction of initiator, which has decomposed uponcompletion of one circulation in the loop reactor is 87.5%,. Preferably,the ratio of the circulation time of the reaction mixture to the halflife time of the initiator is less than 3, more preferably less than 1.Preferably this ratio is at least 0.05 in order to still obtain areasonable molecular weight distribution.

The amount and type of initiator strongly determine the obtainablemolecular weight, of the copolymer of the invention. In general it canbe said that with a lower concentration of I, a higher molecular weightcan be obtained. In this application the molecular weight is the weightaverage molecular weight. The molecular weight is also stronglydetermined by the temperature of the process and to a minor extent bythe solvent and solvent concentration. This holds for the suspension aswell as for the solution process.

The reaction mixture is internally circulated. Generally the processwill be conducted in such a way that the circulation time is between 0.1and 10 minutes. Herewith reasonable reaction times are obtained for theprocess of the invention. To enable shorter times than 0.1 minute higherreactor temperatures should be maintained for a given conversion, withconsequently an additional risk of degradation reactions occurring.Longer times than 10 minutes may cause inefficient use of the processequipment especially when several circulations are applied in theprocess. In the case that the loop reactor comprises two jacketedreactors in a loop, the circulation time is the volume of the jacketedreactors devided by the flow rate per unit of time in the loop. This caneasily be measured by e.g. putting a flow meter in the tube whichconnects the first and the second jacketed reactor. In the case of atank reactor with internal draft tube and helicon mixer, the internalcirculation can be calculated on the basis of the pumping capacity ofthe helicon mixer, which depends upon e.g. on the speed of revolution ofthe helicon mixer and the pitch of the helicon mixer. The calculation ofthe circulation time of a stirred tank reactor with an internal drafttube and helix type mixer is described in detail in U.S. Pat. No.3,392,963.

In the case that the process of the invention is conducted as a solutionprocess, the feed flow to the loop reactor further comprises a solventor a solvent mixture. The solvent or solvent mixture is chosen in such away that the monomers as well as the resulting copolymer of MA and AVEdissolve in it. The amount of the solvent or solvent mixture in thereactor flow is generally chosen between 30 and 65 wt %, based on thetotal weight of the reactor contents. At amounts of less than 30 wt. %the viscosity of the solution will increase making handling in theprocess more difficult, whilst at amounts of solvent above 65 wt % theresulting copolymer is strongly diluted and large amounts of solventhave to be disposed of. Suitable solvents for solution polymerizationaccording to the invention include acetone and methyl ethyl ketone.

In the case that the process of the invention is conducted as asuspension process additional, compared to the amount needed forproducing the copolymer, AVE or a diluent is used to dilute the reactionmixture. The resulting copolymer of MA and AVE does not dissolve in theAVE or the diluent and thereby forms a solid and thus a suspension isobtained. The solid content, comprising at least the copolymer, of thereaction mixture is generally between 10 and 35 wt %. At solid contentsbelow 10 wt % the process will become less efficient while at solidcontents above 35 wt % the transport of the suspension in the processwill become more difficult. Suitable diluents for the suspensioncopolymerization according to the invention include benzene, toluene,ethyl benzene, xylene, heptane, cyclohexane, hexane, diisopropyl ether,tert-butyl methyl ether, dibutyl ether, methyl isobutyl ketone, methylamyl ketone, methyl isoamyl ketone and mixtures thereof. For renderingthe produced copolymer suitable for e.g. use on the human body,preferably aliphatic non-toxic diluents such as heptane, cyclohexane,dilsopropyl ether, tert.-butyl methyl ether, dibutyl ether, methylisobutyl ketone, methyl amyl ketone, methyl isoamyl ketone and mixturesthereof are used. More preferably these aliphatic non-toxic diluents areused in combination with a molar ratio of AVE to MA of higher than 2 inorder to keep the level of unreacted MA in the resulting copolymer low.Preferably AVE is used instead of an additional diluent to dilute themonomer flow. This limits the number of process flows to be controlled.

Another advantage of the process of the invention is that lowerinitiator concentrations than so far used in a batch process can beemployed, which is particularly advantageous for obtaining highermolecular weight copolymers of MA and AVE.

The molecular weight of the copolymer obtained by the process accordingto the invention is generally between 50,000 and 2,000,000 g/mol.Copolymers with lower molecular weights than 50,000 g/mol as well ascopolymers with molecular weights higher than 2,000,000 g/mol are so farof only limited commercial importance.

Through a suspension process copolymers with various molecular weightscan be produced, however this process is preferably used for producingcopolymers with a high molecular weight, between 500,000 and 2,000,000g/mol. Copolymers with molecular weights of less than 500,000 g/mol canalso be produced through a solution process, in which case the molecularweight is preferably between 100,000 and 500,000 g/mol. A molecularweight larger than 500,000 g/mol is generally too viscous for a solutionprocess.

Yet another advantage of the process of the present invention is thatcopolymers with a narrower molecular weight distribution can be obtainedthan in the known batch processes. The molecular weight distribution,Mw/Mn, is the ratio of the weight average molecular weight Mw, to thenumber average molecular weight Mn. The molecular weight of thecopolymer of the invention can be controlled by using the internalcirculation of the reaction mixture. The flow rate per unit of time ofthe internal circulation is defined as the internal circulationF_(ic).Particularly, the molecular weight distribution of the copolymerof MA and AVE can be controlled using the ratio of the internalcirculation F_(ic) to the feed flow F_(f), both expressed as volume perunit of time. F_(ic)/F_(f) is in this application also referred to asthe circulation ratio.

The circulation ratio F_(ic)/F_(f) can be easily determined. The feedflow F_(f) is defined as the volume per unit of time of MA, AVE, I andoptionally solvent or diluent added to the reactor through the inlet.The internal circulation F_(ic) depends on the reactor type. In the caseof a loop reactor comprising two separate jacketed reactors,subsequently connected in a loop, the internal circulation is the flowrate in the loop. In the case of a tank reactor with internal draft tubeand helicon mixer, the internal circulation can be calculated throughthe pumping capacity of the helicon mixer, which depends e.g. on thespeed of revolution of the helicon mixer and the pitch of the heliconmixer. The calculation of both F_(ic) and circulation time is describedin detail in U.S. Pat. No. 3,392,963.

Preferably the circulation ratio is at least 15. Herewith a molecularweight distribution of the resulting copolymer of less than 2.3 can beobtained. An other advantage of a circulation ratio of at least 15 isthat the risk of a runaway reaction is further reduced. More preferablythe circulation ratio is higher than 50. This results in a copolymer ofMA and EVA with a molecular weight distribution of less than 2. Mostpreferably the circulation ratio is between 100 and 300. This results ina copolymer of MA and AVE, with a molecular weight distribution of lessthan 1.9.

In the process of the invention a part of the reaction mixture leavesthe loop reactor. In the reaction mixture still a remainder of initiatoris present. Preferably this remainder is less than 20 mol % and morepreferably less, than 10 mol %. This prevents unwanted side reactions inthe post reactor. Furthermore the reaction mixture leaving the loopreactor still contains unreacted MA. For some applications of thecopolymer according to the invention, e.g. as personal care products, alow level of MA is preferred. This low level of MA is preferably lessthan 10 parts per million, ppm, and more preferable less than 5 ppm.Most preferred is an MA content of less than 1 ppm based on the weightof the total composition, e.g. in those cases where the copolymer maycome into direct contact with the human skin. This level can be reachedwith the process according to the invention wherein the part of thereaction mixture, which has left the loop reactor, is subsequentlyheated e.g. in a postreactor to a temperature between 120 and 220° C.,for a time sufficient to reduce the free MA content to below 10 partsper million, based on the total weight of the reaction mixture. The timenecessary for this treatment depends on the desired level of MAremaining in the copolymer and can easily be determined by the oneskilled in the art.

The remainder of I in the total of the reaction mixture is determined bythe average total residence time of the reaction mixture in the loopreactor. The average total residence time in the loop reactor is thevolume of the loop reactor divided by the feed flow, expressed in volumeper unit of time. Furthermore the remainder of I is determined by itschemical reactivity, expressed as its half-life time, and thetemperature at which the process of the invention is conducted.Half-life time of an initiator in relation to temperature is normallyavailable through the supplier.

Depending on the chosen type of the process of the invention thecopolymer still is in a suspension or in a solution after passing thepost reactor. The suspension and if desired even the solution can betransformed into a powder using the generally known techniques, such asa centrifuge and a dryer, flash vessels and extruders. With thesetechniques the solvent, diluent or excess AVE is separated from thecopolymer of MA and AVE.

The separated solvent, solvent mixture or diluent or excess AVE can bere-used in the process directly or after a purification and separationstep. Generally known techniques such as distillation, cyclones andfilters can be applied.

Surprisingly it has been found that the copolymer of MA and AVE with amolecular weight distribution of less than 2.0 can be used for glueingof human bones.

The present invention therefore also relates to a copolymer of MA andAVE characterized in that the molecular weight distribution, expressedas Mw/Mn, is less than 2.0 and preferably less than 1.9.

The copolymer of MA and AVE can however also be used for otherapplications than glueing of human bones, e.g. the copolymer of MA andAVE is often applied in hygiene and personal care products as well as insurgery products, examples of applications being toothpastes, hairfixatives and glues. For many applications, the copolymers should besoluble in water.

The copolymers produced in the process according to the invention canalso be further modified in either a continuous or a batch wise manner.For instance, the anhydride groups contained in the polymer can behydrolyzed with water to yield carboxylic acid groups. These hydrolyzedcopolymers are used in tooth-paste and mouth-washes, or in adhesives.Alternatively, it is known that hydrolysis of the polymer can beeffected by a caustic aqueous solution to yield alkali or earth-alkalisalts of the carboxylic acid groups containing copolymers.

Preferably the hydrolyzed copolymers are made from copolymer producedaccording to the invention in a solution polymerization process. Theadvantage hereof is that the copolymer solution as obtained can beapplied directly for further modification. More preferably thehydrolyzed copolymers are made in a continuous way by contacting thecopolymers with water in a high-shear mixing device and subsequentlyremoving the solvent or solvent mixture by distillation.

Another known modification of the copolymers is by alcoholysis. In thisreaction the anhydride groups contained in the copolymer are reactedwith lower alkyl alcohols. Suitable examples of lower alkyl alcohols areC₁-C₄ alcohols. The alcohol-anhydride reaction is a fast reaction whichgives one ester group and one carboxylic acid group per reactedanhydride group. The alcohol can also react with the formed carboxylicacid, but this reaction is slower. Alcoholized copolymers of maleicanhydride and alkyl vinyl ether are used e.g. as hair fixatives. Ifethanol is chosen as the lower alkyl alcohol, the modified polymer isusually left dissolved in ethanol with a solid content of about 50 wt.%. If propanol or butanol is chosen as the lower alkyl alcohol, theexcess of alcohol is usually first distilled from the modified polymer,and the modified polymer is again dissolved in ethanol to give a polymersolution with a solid content of about 50 wt. %.

In view of the above, the invention also relates to hydrolyzed oralcoholyzed copolymers of MA and AVE, characterized in that themolecular weight distribution, as expressed as Mw/Mn, is less than 2.0.

Furthermore the invention also relates to an apparatus to carry out theprocess of the present invention. With the apparatus of the inventionthe process can be carried out in a continuous manner. Until today theprocess of the invention only has been carried out only in a batchwiseor semi-batchwise manner.

A further object of the invention is to provide an apparatus forconducting the process of the invention.

This object is achieved through an apparatus for conducting the processof the invention, which comprises a loop reactor, which is connectedthrough a tube to a post reactor, the post reactor being constructed insuch a way that plug flow is obtained.

With the apparatus of the invention the amount of unreacted MA in thereaction mixture can be reduced. The apparatus of the invention isspecially suited for reduction of the level of unreacted MA of less than10 parts per million, ppm, based on the total weight of the reactionmixture. Furthermore it has been found that the apparatus of theinvention is also very suitable for reducing the amount of unreacted MAin other types of copolymerizations. Moreover the apparatus of theinvention has been found to reduce the amount of unreacted monomers incopolymerizations.

In the post reactor plug flow is generally obtained by designing thispost reactor for laminar flow and incorporating static mixing elementsin said reactor. Several static mixing elements can be used, an examplebeing a Sulzer SMXL® element.

Preferably the loop reactor comprises a stirred tank reactor, which isfitted with, a draft tube and a helicon mixer in an annular part and anoptional pitch bladed or MIG mixer. In this way a loop reactor with acompact design is obtained, which requires little room in a plant. Anadded advantage is that this reactor is very suitable for mixing a veryviscous solution or suspension, which is obtained with reaction mixturescomprising copolymers with high molecular weights.

A stirred tank reactor with an internal draft tube and helix type mixeris described in U.S. Pat. No. 3,392,963. In this publication a stirredtank reactor is described which is furthermore fitted with two pitchbladed mixers in the center of the reactor with two separated feedpoints. This reactor relates to the preparation of EPDM rubbers, muchattention being paid to the fact that the reactants are fed separately.It is not suggested that such a reactor is suitable for thecopolymerization of MA and AVE. Moreover if this reactor would be usedfor the copolymerization of MA and AVE, the level of unreacted MA wouldbe too high resulting in an unsuitable copolymer of MA and AVE.

The invention will be elucidated by the following, non limiting,drawings.

In these drawings FIG. 1. gives an example of a schematical layout of afirst embodiment of an apparatus to conduct the process of the inventionfor preparing a copolymer of maleic anhydride and a alkyl vinyl ether,comprising a loop reactor with two separate jacketed reactors and acirculation pump and a post reactor after which the layout of a processfor a suspension process is shown; and FIG. 2. gives an example of aschematical layout of a second embodiment of an apparatus to conduct theprocess of the invention for preparing a copolymer of maleic anhydrideand a alkyl vinyl ether, comprising a loop reactor in the form of astirred tank reactor fitted with a draft tube and in the annular part ahelicon mixer and a post reactor after which the layout of a process fora solution process is shown.

In FIG. 1., 1 is a storage tank for MA, 2 is a storage tank for I , 3 isa storage tank for AVE and 4 is a storage tank for an optional solventor diluent. The storage tanks 2, 3 and 4 are connected through a tube 5to a loop reactor 6. Storage tank 1 is connected through a tube 7 to theloop reactor 6. The loop reactor comprises two separate jacketedreactors fitted in a circulation loop 9, comprising tubes 9 a-9 e. Inthis circulation loop the exit of a first jacketed reactor is fittedwith a tube 9 a to a pump 8 which is connected to the inlet of a secondjacketed reactor with tube 9 b. The exit of the second jacketed reactoris connected to the inlet of the first reactor with tubes 9 c, 9 d and 9e. Furthermore the circulation loop contains a branch between tubes 9 cand 9 d from which tube 11 leaves to a post reactor 12 and contains asecond branch between tubes 9 d and 9 e to which tubes 5 and 7 areconnected. The post reactor is fitted with a heating device and isfitted through a tube 13 to the purification or separation part of theprocess. The purification part starts with a centrifuge 14. Thecentrifuge 14 is connected with tube 15 to a dryer 17. Furthermore thecentrifuge 14 is fitted through a tube 16 to a separation unit 21, whichis fitted with a tube 22 to storage tank 3 and with tube 23 to storagetank 4. Dryer 17 is fitted through a tube 18 and a condenser 20, to theseparation unit 21. Finally the drier is fitted with a tube 19 fromwhich dried copolymer of MA and AVE according to the invention isobtained.

In FIG. 2., 201 is a storage tank for MA, 202 is a storage tank for I,203 is a storage tank for AVE and 204 is a storage tank for an optionalsolvent or diluent. The storage tanks 201, 202, 203 and 204 areconnected through tube 205 comprising a cooler 206 to a stirred tankreactor 207. The storage tank for MA is connected with a tube 208 to thestirred tank reactor 207. The stirred tank reactor is fitted with anoptional pitch bladed or MIG mixer 209, a draft tube 210 and a heliconmixer 211 in an annular part. A tube 212 is leaving the reactor andforms an input to a post reactor 213 which can be heated. A tube 214 isleaving the post reactor 213 to the purification or separation part ofthe process. The purification part starts with a flasher 215 of which atube 216, which contains a flow of a concentrated solution, is leavingto an extruder 217. A tube 218, through which off gasses from theextruder flow, and a tube 219, through which off gasses from the flasher215 flow, are led to a condenser 220, after which a separation unit 221is placed. From the separation unit a tube 222 is returned to storagetank 203 and a tube 223 which is returned to the storage tank 204.Finally a tube 224 is leaving the extruder from which the copolymer ofMA and AVE according to the invention is obtained.

1. Process for the preparation of a copolymer of maleic anhydride and analkyl vinyl ether, comprising the steps of supplying maleic anhydrideand the alkyl vinyl ether and an initiator, together forming a feedflow, through an inlet to a reactor wherein maleic anhydride and thealkyl vinyl ether react to a copolymer of maleic anhydride and alkylvinyl ether which forms a reaction mixture with the maleic anhydride,the alkyl vinyl ether and the initiator, characterized in that theprocess is a continuous process and the reactor is a loop reactor,optionally followed by a postreactor, wherein the reaction mixture isinternally circulated, whereby this reaction mixture arrives again atthe inlet before the maleic anhydride and alkyl vinyl ether havecompletely reacted and while a remainder of initiator is still present.2. The process of claim 1, wherein the feed flow to the loop reactorfurther comprises a diluent, a diluent mixture a solvent or a solventmixture.
 3. Process according to claim 1, wherein the feed flowcomprises a molar ratio of maleic anhydride to initiator of between 100and 10 000
 4. Process according to claim 1, wherein the feed flowcomprises a molar ratio of alkyl vinyl ether to maleic anhydride ofbetween 1.05 and 5
 5. Process according to claim 1, wherein the alkylvinyl ether is a C1-C4 alkyl vinyl ether.
 6. Process according to claim1, wherein the process is carried out at a temperature between 50° C.and 180° C.
 7. Process according to claim 1, wherein the ratio of aninternal circulation to the feed flow is at least
 15. 8. Processaccording to claim 1, wherein a part of the reaction mixture issubsequently heated to a temperature between 120 and 220° C., for a timesufficient to reduce the free MA content to below 10 parts per million,based on the total weight of the reaction mixture.
 9. Copolymer ofmaleic anhydride and alkyl vinyl ether, wherein a molecular weightdistribution, expressed as Mw/Mn, is less than 2.0.
 10. Hydrolyzed oralcoholized copolymer of maleic anhydride and alkyl vinyl ether, whereinthe molecular weight distribution, expressed as Mw/Mn, is less than 2.011. Apparatus for conducting the process of claim 1, which comprises aloop reactor which is connected through a tube to a post reactor thepost reactor being constructed in such a way that plug flow can beobtained.
 12. Apparatus for conducting the process of claim 9, the loopreactor comprising a stirred tank reactor (207) which is fitted with anoptional pitch bladed or MIG mixer (209), a draft tube (210) and ahelicon mixer (211) in an annular part.